BARRETT 900 SERIES TRANSCEIVERS
4.5 Remote control head
The on/off switch on the volume control potentiometer completes the circuit to ground and activates the
power relay on the PA in the transceiver's main body through the remote control cable via line RH PWR SW.
In addition the on/off switch turns on Q6 allowing +14 V power feed to the regulators U7 and U6. The 5 V
regulator U6 supplies the digital ICs and the second 5 V regulator U7 is stacked on the first to obtain 10 V for
the analogue circuit.
Keyboard encoding is handled by U2, a matrix encoder chip that provides a PWM coded output only when a
key is depressed. The microphone up and down buttons are also handled by U2.The serial output from U2 is
buffered by FET Q8 and emerges at connector P1 as RH SKB OUT for eventual decoding by the
microprocessor.
Serial data from the transceiver's main body is sent to the remote head on line RH SD INB via the remote
head interface cable. This serially coded data is decoded by embedded microprocessor U1 and distributed
in parallel form to either the LCD or mode and status LED's as required. LCD contrast is temperature
compensated by thermistor TH1. Q1 switches the LCD and keypad back-lighting on and off by computer
control.
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